Water-containing polymeric products such as waterborne paints, stains, adhesives, printing inks and coatings find increasing utility because of their safety, economy and ease of application. However, the drying characteristics of such products are variable and cannot be easily controlled, because they are basically limited to the evaporation characteristics of water. Thus, the drying behavior of aqueous polymer products is highly dependent on the conditions of temperature, humidity and air velocity. For example, coating films of such products can dry practically instantaneously under hot, dry, windy conditions leading to poor lapping characteristics. Further, such drying conditions tend to impair the quality of film formation, penetration of and adhesion to the substrate.
Polymeric compositions borne in organic solvents are different from the waterborne products, in that solvents or solvent blends with a wide range of boiling points and volatility can be used to control the drying characteristics according to application requirements. For example, consumer paints employing alkyd resins are made with hydrocarbon solvents of volatility selected such that the drying rate is sufficient to allow setting of the film to minimize sagging, running, and dust pickup, yet which permits good "melting in" of paint at overlapping brush or roller strokes. The disadvantages of such organic solvent based compositions are the difficulties of clean-up, the toxic nature of organic solvents, environmental pollution, and the relatively high cost of organic solvents which are ultimately wasted.
The conventional practice in solving the drying rate problems of water-based compositions is to add substantial levels of water soluble solvents to such systems to increase the wet-edge or open time. These techniques are discussed by M. D. Andrews, "Influence of Ethylene and Propylene Glycols on Drying Characteristics of Latex Paints," Journal of Paint Technology, vol. 46, page 40 (1974); D. A. Sullivan, "Water and Solvent Evaporation from Latex and Latex Paint Films," Journal of Paint Technology, vol. 47, page 60 (1975); and C. R. Martens, Waterborne Coatings, Van Nostrand Reinhold, page 153 (1981). These references disclose the use of short chain water-soluble alcohols and glycols as cosolvents for water-based coatings to improve freeze-thaw stability, aid coalescence of the latex particles, improve leveling, etc., in addition to prolonging wet-edge or open time. To obtain significant improvement in wet-edge or open time, high levels of these low molecular weight cosolvents are required, often 10 to 20 percent or more based on total volatile content, since they are believed to function simply by being completely soluble in water; thus reducing the vapor pressure of water. These cosolvents exhibit low surface activity, and the use of high levels tend to negate the intrinsic advantages of the water-based compositions.
The use of evaporation retarders on the surface of reservoirs to control water evaporation is known in the art. The evaporation retarders are typically aliphatic alcohols and ether alcohols containing 16 to 30 carbons, such as described in U.S. Pat. No. 3,146,059 and Indian Pat. No. 70,670. The use of these long chain alcohols as surface monolayers on water is further discussed by E. R. Noe and R. G. Dressler, "Performance of Odd and Even-Chain Pure Alcohol Monolayers in Water Evaporation Retardation," I & EC Product Research and Development, vol. 6, page 132 (1967) and in other literature. Although these long chain alcohols and ether alcohols have been effective on relatively pure water due to their surface activity, their utility in multi-component, water-based polymeric compositions had not previously been recognized or discovered.
U.S. Pat. No. 2,965,678 discloses the use of branched-chain alcohols as wetting agents and detergents. However there is no teaching or suggestion that unbranched-chain compounds are effective for water evaporation retardation in aqueous polymer compositions.
U.S. Pat. No. 3,287,300 teaches the use of aliphatic carboxylic acids in polyvinyl ester emulsions to lower the coalescense temperature. The '300 patent teaches nothing about evaporation suppression and the importance of using C.sub.16 -C.sub.24 aliphatic straight-chain compounds to reduce water evaporation from polymer compositions.
U.S. Pat. No. 3,553,123 discloses cleaning and polishing compounds which are emulsions of natural and synthetic waxes and resins, and which contain very large quantities (i.e. 40-50%) of volatile organic solvent. Moreover, the emulsifiers disclosed in the '123 patent would not be effective as evaporation suppressants because they are referred to as being highly branched, having a relatively low number of carbon atoms (i.e. 12-18), or having a high number of oxyethylene units.
U.S. Pat. No. 3,847,855 discloses a latex polymerization process which uses a volatile surfactant for the polymerization. The '855 patent teaches nothing about evaporation suppression, and there is no teaching or suggestion that any of the diverse surfactants mentioned would be effective in retarding evaporation of water. Rather, the fugitive surfactants described in the '855 patent are used as an ingredient during the polymerization process.
U.S. Pat. No. 3,988,275 discloses a polymerization process for making concentrated latex of synthetic rubbers using emulsifying agents such as fatty acids. Methods to achieve suppression of evaporation rate of water from the latex formulations are not taught or implied. The emulsifiers disclosed in the '275 patent are generally not suitable for evaporation suppression because they are generally too asymetrical and of relatively short chain length.
U.S. Pat. No. 4,131,585 discloses plasticizer-type leveling agents for floor polish emulsions. The leveling agents are required to contain either nonlinear alkyl or alkylbenzene hydrocarbon groups, and would therefore not be suitable evaporation suppressants because they do not form compact surface films to retard water evaporation. Moreover, they are required to contain 15 or less carbon atoms in the alkyl chain. The '585 patent specifically teaches against the use of linear alcohol derivatives.
U.S. Pat. No. 4,330,338 discloses emulsions in water of resins dissolved in organic solvent for use as pharmaceutical coating compositions. The '338 patent teaches or suggests nothing regarding the selection of surfactants except that they are to assist in producing a stable emulsion. Nothing is taught or suggested concerning their surface activity or effect on water evaporation. The fatty alcohol ethoxylates disclosed as emulsifiers have only lauryl (12 carbon atoms) hydrophobes, and generally have too excessive a degree of ethoxylation for use as effective evaporation suppressants.
U.S. Pat. No. 4,454,260 discloses suspensions of water-soluble polymers in organic solvent and the use of surfactants therefor. Such materials are then later dissolved in water to make a polymer solution for oil recovery from wells. The '260 patent is totally unrelated to the use of long straight-chain aliphatic compounds for reduction in evaporation rate of water from waterborne polymer compositions. Rather the '260 patent teaches the use of alkali or alkaline-earth metal salts of fatty acids as thickener for the suspensions of water-soluble polymers in organic solvent.
Applicants have surprisingly discovered that low levels of surface active, long chain, aliphatic hydrocarbon-type compounds can be used to control and improve the drying characteristics of aqueous-based polymer compositions. These long chain aliphatic compounds are effective as evaporation suppressing agents at levels as low as 1% by weight or less. Their effectiveness is believed to be attributed to their ability to become highly concentrated and compactly ordered at the air/water interface, even when initially uniformly mixed into the aqueous-based polymer compositions.
It is the object of this invention to provide a method for reducing the evaporation rate of water from aqueous polymer compositions using low levels of surface active, long chain, unbranched aliphatic compounds. It is also an object of this invention to extend the wet-edge or open time of aqueous-based coatings and the like when applied to a substrate. It is a further object of the invention to reduce skinning of waterborne polymer compositions in containers, and to retard drying out on application equipment such as rollers and brushes. It is an even further object of the present invention to improve the quality of film formation/adhesion of aqueous polymeric coatings by incorporating therein low levels of surface active evaporation suppressants.